The present invention relates to a simple low-cost apparatus for low-rate tensional fatigue testing of multiple specimens. Most fatigue testing equipment available to date has been limited to heavy expensive indoor laboratory equipment that can test, at best, two specimens simultaneously.
In accordance with the invention, a single apparatus can be built to test a large number of specimens simultaneously at a low unit cost per test station, and in an outdoor environment. The new apparatus comprises: a rigid support frame; a plurality of test stations mounted on the frame; a source of air pressure and a manifold for conducting air from the source to the test stations; a voltage source; and a program timer switch comprising a plurality of switch contacts, one for each test station, and means for connecting one side of the voltage source to each of the contacts in a predetermined sequence. Each test station includes: a first specimen holder attached to the support frame; an air cylinder attached to the frame and having a piston to which a second specimen holder is attached; a solenoid valve having an air inlet connected to the manifold, an air outlet connected to the air cylinder and two electrical terminals; a single-pole-single-throw test terminate switch having two terminals and an actuating lever adapted to open the switch when the specimen fails, one of the switch terminals being connected to the other side of the voltage source, and the other switch terminal being connected to one terminal of the solenoid valve; and means connecting the other solenoid valve terminal to one of the contacts of the timer switch, to complete the circuit from the voltage source to the solenoid valve, whereby the failure of one specimen during testing interrupts the circuit of its station only. Preferably, an electrical elapsed-time indicator is connected in parallel with the solenoid valve and timer switch contacts and in series with the test terminate switch, in each station.